It is desirable when dispensing liquids, including viscous fluids and slurries, to limit the dispensing to a pre-determined volume or amount without leakage or seepage of liquid following completion of dispensing. Effective control over the dispensing of liquids avoids waste and reduces the amount of residue remaining on the dispenser following completion of dispensing. Such control also avoids imparting unintended characteristics to the material, composition or process as a result of receiving greater than intended amounts of liquid from the dispensing device.
It is also often desirable when dispensing liquids, slurries and viscous materials to obtain a relatively uniform or pre-determined distribution of the dispensed liquid. Condiments such as ketchup, mustard and mayonnaise, for example, when dispensed commercially on prepared food items, are preferably dispensed relatively uniformly over the surface of the prepared food item.
Previous liquid dispensers often consisted of either deformable or rigid containers fitted with a nozzle or opening. Deformable containers typically dispense when pressure is applied to the containers' walls. Rigid dispensers typically dispense when pressure is applied directly to the contents of the package or to a non-rigid portion of the container. A plunger or other pressure generating device acting on the contents of the rigid package through an aperture in the package, for example, can actuate dispensing.
Both deformable and rigid packages containing liquid to be dispensed are typically fitted with end caps, nozzles or other openings to allow passage of the dispensed liquid in response to pressure applied to the package or its contents. Often these end caps, nozzles or openings fail to effectively cut off passage of the dispensed liquid when the applied pressure is removed, allowing unintended leakage or seepage of the liquid dispensed.
As a result of such leaking or seepage, a portion of the liquid can form a residue on the nozzle or other opening in the package.
With the passage of time, this residue can accumulate or cake on the nozzle or other opening. This, in turn, can result in clogging, impeding later efforts to dispense through the nozzle or opening. While such residue can be removed manually, manual removal may occur irregularly and be ineffective. Commercial users of dispensers, such as restaurants, also face added costs if employees must devote time to removing residue from dispensers. In addition, even with removal of this residue, wastage caused by excess dispensing will remain.